1. Field of the Invention
The present invention relates to 2,4,8,10-tetroxaspiro[5.5]-undecane(pentaerythritol diformal) and more particularly to an improved method for its preparation.
2. Description of the Prior Art
Pentaerythritol diformal is readily prepared, often in good yield, under acidic conditions from pentaerythritol and aqueous formaldehyde, trioxane, or paraformaldehyde. Reaction times, however, are in the order of several hours or days, and operations for its isolation can be time-consuming. These conventional processes may be illustrated by that of A. Skrabal et al [Z. Physik. Chem., 119, 305 (1926)] which consists in heating pentaerythritol in trioxane, on a waterbath, for 4 hours in order to obtain a 75% yield of the spirocyclic formal. Formation of the diformal from chloromethyl ethers of pentaerythritol and of 5,5-bis(hydroxymethyl)-1,3-dioxane has no practical synthetic value [J. Lichtenberger et al, Bull. Soc. Chim. France, 468 (1947)]. As to the reaction of paraformaldehyde with paraldehyde to obtain the diformal, it requires at least 30 hours for a 15% yield by tedious operations [H. J. Prins, Rec. Trav. Chim. 71, 1131 (1952)].
The more recent efforts in the preparation of various acetals of pentaerythritol still offer no clues on the possible improvement of the conventional preparations of pentaerythritol diformal. Renner et al (U.S. Pat. No. 3,978,088), for instance, prepare diacetals with dimeric .beta.-OH-pivaldehyde in hydrochloric acid by a 24 hour reaction. Fruhstorfer et al (U.S. Pat. No. 3,621,034), on the other hand, boil pentaerythritol with dodecylthiopropanol for 31/2 hours, while Kray et al (U.S. Pat. No. 2,915,530) obtain their diacetals with e.g. acrolein after a 4 hour reflux period in the presence of 0.1% phosphoric acid.
Finally, Zey et al (U.S. Pat. No. 4,076,727) most recently disclosed the preparation of cyclic acetal from polyols, e.g. trimethylolpropane and an aldehyde such as formaldehyde and butyraldehyde, by refluxing such compounds in, e.g. benzene for a period of at least 4 hours. The possibility of higher temperatures, i.e., up to 150.degree. C., is mentioned, solvent permitting it is assumed. In any event, Zey et al appear to be committed to a conventional process to obtain the acetals that they need for the synthesis of acrylic esters.
In summary, the processes that have just been reviewed, as well as several other existing approaches, variously suffer from one or more of the following shortcomings, namely: long reaction times--hours or days; inferior yield of product; time-consuming procedures for isolation; use of solvents; high expenditure of energy; and inadaptability to continuous production.
In view of this situation, it is the principal object of this invention to provide a process which will be free of any and all of the art limitations just enumerated.